I had to edit /usr/share/mime/packages/freedesktop.org.xml and add some globby looking stuff. I ran a command I've never seen before, "sudo update-mime-database /usr/share/mime". And now my cgi and custom extensions open with the correct coloring in gedit, my gui text editor of choice. I made .cgi be a python file and .template and .x be html files.

Not sure what any of that had to do with gedit, but it works. Why wasn't this a setting within gedit, I'll never know. I guess this is a system-wide change I've made, that will effect my vim editor too.